1. OBJECTIVE : Thermal properties, especially, thermal conductivity and apparent viscosity of drilling mud under high temperatures and pressures are needed to analyze the temperature change of the mud circulating in the mud drilling line in high temperature reservoirs and to estimate early virgin strata temperatures around the well drilled. Mud used in exploration and production wells are almost universally water-based mud consisting dispersions of colloidal clay in fresh water and some peptizers. As the results of the constituents, the mud are electrolyte. Objective of this research is to develop a measurement system of the thermal conductivity of the bentonite mud and to evaluate the change of the value with the concentration and temperature, so on. of the mud.2. RESULTS in Fiscal 1989 : Twin needle probe type apparatus to cancel the end effects in the measurement was developed using Inconel 600 sheath K-thermocouple wires with 0.65mm O. D. and 0.07mm wall thickness. Test results sho
… Morewed that thermal conductivity, lambda, of pure bentonite mud increased with increasing the mud concentration and temperature in lower temperatures than 100^ﾟC of the mud autoclaved ones [0.7 at 20^ﾟC to 0.85W/(m・K) at 250^ﾟC], however, lambda of it decreased with mud temperature in the case of the mud autoclaved one equal to 200^ﾟC. Accuracy of the measurements are estimated as <plus-minus>7.0%.3. RESULTS in Fiscal 1990 : Twin thin platinum wires of U-character-shape type apparatus was developed to measure lambda more accurately. Diameter of the platinum wire is 40 mu m and it is coated with 6 mu m thickness polyamide-imide layer. Measurement errors were estimated as <plus-minus>3.2% for pure water of temperatures from 25 to 50^ﾟC and <plus-minus>3.8% for glycerol of temperatures from 25 to 150^ﾟC. Reproducibility of the experimental values of lambda at 20^ﾟC of the mud having 10% concentration was <plus-minus>1.7% and the mean value was 0.537W/(m・K). It is the subject for a future study to simplify the measurement operation with maintaining the high accurately. Less